Mechanism of first order

Repeated attempts in this laboratory to demonstrate the presence of unpaired electrons in polyacrylonitrile initiated by AIBN at 50°C., using a Varian spectrometer, have failed to detect any signal at all. Measurements have been made both at room temperature and at —196 °C., and we believe that we could have detected concentrations as low as 1014 radicals per ml. Hence, it is not possible under the conditions reported here to account for the kinetic results by the mechanism of first-order termination of growing chains by entrapment in precipitated polymer. This is not to say, however, that under other conditions, such as photo-initiated polymerization at low temperature, the trapped radicals are unimportant to the kinetics of polymerization. 

TABLE 1. Comparison of the two fundamental mechanisms of first-order phase transitions... 

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